Microwave horn aerial with spiral corrugated inner surface

ABSTRACT

A microwave horn aerial is corrugated on its inner surface by being formed, e.g. by a screw cutting operation with a single start spiro helical groove or by moulding on a mandrel. In the latter case manufacture is relatively easy because the mandrel can be withdrawn by unscrewing it.

O United States Patent 1 [111 3,732,571 Neale 1 May 8, 1973 [54]MICROWAVE HORN AERIAL WITH SPIRAL CORRUGATED INNER [56] References CitedSURFACE UNITED STATES PATENTS [75] Inventor: Noel William Thomas Neale,Hal- Stead England 2,856,605 l0/l958 Iacobsen ..343/895 2,863,14812/1958 'Cammon et al. .343/895 [73] Assignee: The Marconi CompanyLimited, Es-

sex, England Primary Examiner-Eli Lieberman Filed Nov 5 1971Attorney-Donald M. Wight et al.

[21] Appl. No.: 196,085 [57] ABSTRACT A microwave horn aerial iscorrugated on its inner [30] Foreign Appli tio Pri it D t surface bybeing formed, e.g. by a screw cutting operation with a single startspiro helical groove or by NOV. 24, I970 Gl'Cfl-t Bntam ..55,767I70 l gon a mandrel In the latter case manufacture is relatively easy becausethe mandrel can be (gill ..343/7::S6134i;g3 withdrawn by unscrewing it q[58] Field of Search ..343/786, 895 6 Claims, 4 Drawing FiguresMICROWAVE HORN AERIAL WITH SPIRAL CORRUGATED INNER SURFACE Thisinvention relates to microwave horn aerials, that is to say to microwaveaerials constituted by tapered lengths of wave guide or flared ortapered dishes. More specifically, the invention relates to so-calledcorrugated microwave horn aerials, by which expression is meant, in thisspecification, internally grooved or ringed microwave horn aerials.

A typical known corrugated microwave horn aerial is shown in sectionalelevation and end view respectively in FIGS. 1 and 2 of the accompanyingdrawings.

Referring to these figures, a length of wave guide 1 opens into a flaredor conical horn 2. A plurality of annular inwardly projecting rings Rare formed on the inner wall of the horn 2. The principal advantageobtained by providing these rings is, as is known, that they result in aconsiderable reduction of side-lobes and frequency-dependent distortionas compared with an otherwise similar horn having a smooth interiorsurface. The underlying theory and explanation of the obtaining of thisadvantage is somewhat complex but, for an understanding thereof,reference is directed to small aperture, small flare angle corrugatedhorns by Bahret and Peters, I.E.E.E. Transactions on Antennae andPropagation, July 1968.

Corrugated microwave horn aerials as at present known have, however, theimportant defect of being expensive to manufacture, as will be apparentfrom a consideration of FIGS. 1 and 2. Indeed, the cost of making anaerial as shown in FIGS. 1 and 2 is such that, in many cases, internallysmooth horn aerials are adopted despite their inferiority electricallyto a horn aerial, as shown in the said FIGS. 1 and 2. Especially doesmanufacture become costly and difficult when the horn taper is small,the nom long and the number of rings large.

The present invention seeks to provide improved microwave horn aerialswhich shall be as good as or at any rate comparable in their radioqualities with known microwave horn aerials but shall nevertheless besubstantially less expensive to manufacture.

According to this invention, a microwave horn aerial is corrugated byforming or otherwise providing the inner surface thereof with at leastone Spiro-helical groove or projection.

Preferably there is only one groove or projection but there may be twoor more in two-or multi-start arrangements.

It will be appreciated that the invention enables a corrugated microwavehorn aerial to be manufactured in a relatively cheap and easy manner,for example, by using a simple screw cutting technique. Again, in thecase of an aerial formed by casting, moulding or spray forming on a coreor mandrel, manufacture is cheapened because the core or mandrel doesnot have to be collapsed to be withdrawn but can be withdrawn byunscrewing it.

The invention will be further described and illustrated by way ofexample with reference to FIGS. 3 and 4 of the accompanying drawingswhich are respectively a sectional elevation and end view of oneembodiment of the invention.

Referring to FIGS. 3 and 4 a length of wave guide 1 opens into aflaredor conical horn 2. The inside wall of the horn 2 [8, however, corrugatedby being formed,

e.g. by a screw-cutting type of operation, with a singlestartSpiro-helical groove S. Despite its simplicity and relative cheapness ofmanufacture, the radio performance of a horn aerial as shown in FIGS. 3and 4 is as good as, or acceptably nearly as good as that of anotherwise comparable horn aerial as shown in FIGS. 1 and 2.

I claim:

1. A corrugated microwave horn aerial comprising a horn body having aninner surface defining a tapered waveguide, and means on said innersurface for reduction of side lobes and frequency distortion ofmicrowave energy propagated therefrom, said means comprising at leastone Spiro-helical projection on said inner surface.

2. A corrugated microwave horn aerial as defined in claim 1 wherein saidprojection is of substantially uniform height throughout.

3. A corrugated microwave horn aerial comprising a horn body having aninner surface defining a tapered length of waveguide adapted to becoupled at the smaller end thereof to a source of microwave energy, andat least one spiro-helical projection on said inner surface.

4. A corrugated microwave horn aerial as defined in claim 3 wherein saidprojection extends substantially from said smaller end of the waveguideto the opposite larger end thereof.

5. A corrugated microwave horn aerial as defined in claim 4 wherein saidprojection is of substantially uniform height throughout.

6. A corrugated microwave horn aerial as defined in claim 3 wherein saidprojection is of substantially uniform height throughout.

1. A corrugated microwave horn aerial comprising a horn body having aninner surface defining a tapered waveguide, and means on said innersurface for reduction of side lobes and frequency distortion ofmicrowave energy propagated therefrom, said means comprising at leastone spiro-helical projection on said inner surface.
 2. A corrugatedmicrowave horn aerial as defined in claim 1 wherein said projection isof substantially uniform height throughout.
 3. A corrugated microwavehorn aerial comprising a horn body having an inner surface defining atapered length of waveguide adapted to be coupled at the smaller endthereof to a source of microwave energy, and at least one spiro-helicalprojection on said inner surface.
 4. A corrugated microwave horn aerialas defined in claim 3 wherein said projection extends substantially fromsaid smaller end of the waveguide to the opposite larger end thereof. 5.A corrugated microwave horn aerial as defined in claim 4 wherein saidprojection is of substantially uniform height throughout.
 6. Acorrugated microwave horn aerial as defined in claim 3 wherein saidprojection is of substantially uniform height throughout.